Blade stalk cover plate



Jan. 24, 1967 R. c. GOODERUM 3,300,179

BLADE STALK COVER PLATE Filed April 22, 1966 I N VENTOR.

A T TORNEY United States Patent 3,300,179 BLADE STALK COVER PLATE Reuben C. Gooderum, Indianapolis, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Michigan Filed Apr. 22, 1966, Ser. No. 544,468 9 Claims. (Cl. 253--77) My invention relates generally to gas turbine engines and more particularly to the rotors of a gas turbine engine. One type of gas turbine rotor comprises a wheel having axial grooves in its rim and a number of blades having so-called fir tree roots Which are matingly received in these axial grooves. A problem associated with this type of blade attachment is caused by the environment of the rotor. Namely, the rotor operates with asubstantial pressure ditferential across it. Consequently, there is a tendency for air to leak through the attachment region of the rotor, that is, through the spaces between the blade stalks and to some extent through the spaces between the blade mounting slots and the fir tree roots. Therefore, it is necessary, in many instances, to provide a cover plate for this region of the rotor to minimize the air leakage. The cover plate may also prevent axial movement of the blades within the blade mounting slots.

The cover plate, like other parts of rotating turbomachinery, is subject both to thermal expansion and centrifugal force. The thermal expansion becomes more troublesome since the cover plate usually expands at a different rate than the wheel. Accordingly, my invention is directed toward providing a segmented cover plate for the annular blade mounting region of a gas turbine rotor which allows for differential thermal expansion between the cover plate and the rotor and in which the centrifugal force acting on the segment aids in effecting a good seal between the segments.

Another object of my inevntion is to provide such a segmented cover plate which also may be utilized to axially locate the blade roots with respect to the wheel.

The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawings in which:

FIGURE 1 is an elevation partially in cross section of a gas turbine rotor provided with a front cover plate in accordance with a first embodiment of my invention and a rear cover plate in accordance with a second embodiment of my invention.

FIGURE 2 is a section taken along the line 22 of FIGURE 1 looking in the direction of the arrows.

FIGURE 3 is an exploded perspective view of a cover plate in accordance with the first embodiment of my invention.

FIGURE 4 is a section taken along the line 4-4 of FIGURE 2 looking in the direction of the arrows.

FIGURE 5 is a section taken along the line 55 of FIGURE 1 looking in the direction of the arrows.

Referring now to the drawings and more particularly to FIGURES l and 2, I have shown a turbine rotor indicated generally at 12 comprising a wheel 14 having a number of circumferentially spaced blades 16 with conventional fir tree roots 18 mounted in axial slots in the periphery of the wheel 14. Also shown is an annular spacer element 20 which abuts the right or downstream side of the wheel for reasons which will become more fully apparent hereinafter.

Each blade 16 has a platform 22 radially outwardly of its root 18 connected to the root by a stalk 23 and the blade mounting region encompasses the annular space bounded by the inner surface of the platforms 22 3,390,179 Patented Jan. 24, 1967 of the several blades and the shouldered outer edge 24 of the wheel 14 below the mounting slots. Since this wheel is subject to a pressure differential across it, there will be an appreciable amount of air through the blade mounting region between the stalks 23 and to some extent between the relatively loose fitting roots within the mounting slots. Therefore, it becomes necessary to provide a cover plate or air seal for this region.

Referring now to FIGURE 2, the front cover plate 26 is seen to comprise a number of segments which when fitted together form an annulus. More specifically, the cover plate 26 is shown as comprising six longer arcuate segments 28 alternated with six shorter somewhat triangular arcuate segments 30. As shown, both end or radial walls of each of the segments 28 and 30 are skewed with respect to a radius of the wheel. The end walls on each segment are oppositely skewed and abut adjacent end walls to form a line contact therebetween as at 32.

Referring now to FIGURE 3, which shows an exploded perspective of the cover plate 26, it is seen that the inner circumferential region of each of the segments 28 and 30 is castellated, forming a number of circu-mferentially spaced lugs 34. Each of the longer segments 28 is provided with a central lock tab 36 disposed between two adjacent lugs 34. As is apparent from FIGURE 4, the wheel rim 24 has an L-shaped flange 38 on its forward face which forms a radially outwardly opening groove 40. The radial wall on the flange 38 is castellated to provide oircumferentially spaced lugs 42; the space between these lugs corresponding to the width of the lugs 34. An in'wardly opening groove 44 in axial alignment with the groove 40 is provided on the left end of each of the blade platforms 22 as viewed in FIGURE 1.

Assembly of the front cover plate is accomplished in the following manner. Each segment of the cover plate is inserted into the grooves 44 in a corresponding number of blades 16. The segment is adjusted with respect to the blades 16 so the lugs 34 on the bottom of the segment align with the spaces between the lugs 42 on the wheel 14 when the blade roots 18 are aligned with the mounting grooves on the rim of the rotor 14. The roots with the segments thus assembled to the blades 16 are then inserted axially into the mounting slots in the rim of rotor 14 until the lugs 34 pass through the opening between lugs 42 and are received in the groove 40. This procedure is repeated until all blades and cover plate segments are mounted on the wheel 14. Then the cover plates are rotated slightly until the lugs 34 are behind the lugs 42. After the segments have been rotated, one of the lock tabs 36 is bent downwardly from the dotted line position shown in FIGURE 4 to the solid line position Where it is disposed between two adjacent lugs 42. This prevents circumferential movement of the segment 30 with respect to the wheel 24. Since each of the segments abuts adjacent segments, it is necessary to locate only one segment circumferentially.

Referring now to FIGURE 5, the second modification utilized in the rear cover plate 46 is shown. An inwardly opening groove 48 is provided in the downstream or righthand end of the blade platforms 22 while the outwardly opening groove 50 is provided at the junction of the wheel 14 and the spacer 20. As before, the cover plate 46 com prises six larger arcuate segments 52 alternated with six smaller triangular segments 54. Since the groove 50 is formed by adding the spacer on the wheel 24, the segments are mounted to the rotor wheel 14 after the blades 16 and front cover plate 26 have been assembled. The rear cover plate segments are mounted by moving them axially and radially into abutment with the aft surfaces of the blade roots 18 and the bottoms of groove 48. The spacer 20 is then added to form the groove 50 and hold the bottom edges of the segments in assembly. Therefore,

castellations on the inner circumferential regions of the rear segments are not necessary. The means utilized to circumferentially locate the rear cover plate 46 comprises a stud 58 on one of the longer segments 52 which is disposed in a mating hole 60 provided in the wheel rim 24 between two blade mounting slots.

The cover plates thus assembled not only locate the blades 16 axially with respect to wheel 14 but more importantly, they provide an effective seal for the blade mounting region to prevent air fiow through the region. This seal is maintained effective under operating conditions which produce varying degrees of differential thermal expansion. Under operating conditions, the cover plates 26 and 46 are hotter than the wheel 14. Therefore, their circumferential growth is greater than that of the blade mounting region in general and the circumferential growth of the bottom of groove 48 in particular. Since both cover plates operate in the same manner, an explanation of the thermal growth accommodation of the rear cover plate 46 only will be given and in connection with FIG- URE 5. In order for the hot cover plate 46 to fit in the smaller circumferential envelope provided by groove 48, the smaller triangular segments 54 move radially with respect to the larger segments 52. This action reduces the outer circumference of the cover plate by reducing the distance between the larger segments 52. The larger segments 52 do not move radially because they are bottomed out against the groove 48 and are held there by the centrifugal force acting on them. Centrifugal force acting on the triangular segments 54 even though of smaller magnitude urges them outwardly against the thermal forces urging them inwardly. The triangular segments thus act as a wedge which maintains an effective sealing contact between the segments without overstressing, the segments.

Thus it can be seen that I have provided two embodiments of a segmented cover plate for the axial blade mounting region of a gas turbine rotor which allow for differential thermal expansion between the cover plate and the rotor, while maintaining an effective seal between the segments.

It will be appreciated that the above described preferred embodiment of the invention may be modified within the scope of the appended claims.

I claim:

1. A bladed rotor comprising in combination:

a rotor having a rim with a plurality of circumferentially spaced generally axial fir tree grooves,

a plurality of blades having fir tree roots mounted in said grooves, each of said blades having a radially inwardly opening groove spaced radially outwardly of its root,

an axially extending circumferential flange on said rim spaced inwardly of said mounting grooves, an annular cover plate mounted on said rotor and having its outer margin disposed in said blade grooves and its inner edge adjacent said flange, said cover plate comprising a plurality of arcuate segments, each of said segments having end surfaces abutting end surfaces on adjacent segments to form a continuous annulus, at least one of said end surfaces on each of said segments being skewed with respect to the radius of said rotor and abutting a mating skewed end surface on an adjustment segment whereby said cover plate accommodates differential thermal growth between said cover plate and said rotor and blades.

2. The bladed rotor as defined in claim 1 wherein both ends of said segments are skewed with respect to said radius.

3. The bladed rotor as defined in claim 1 wherein said arcuate segments consist of elongated segments alternated with shortened generally triangular segments.

4. The bladed rotor as defined in claim 3 wherein said arcuate segments have both ends skewed with respect to said radius and wherein the ends of each segment are oppositely skewed.

5. The bladed rotor as defined in claim 4- including a radical wall on said flange to define an annular groove opening toward the grooves in said blades, said segments having their radially inner margins disposed in said annular groove.

6. The bladed rotor as defined in claim 5 wherein at least one of said segments includes means to prevent relative rotation between it and said rotor.

7. The bladed rotor as defined in claim 5 wherein said radial walls are castellated and wherein the inner margins on said segments are matingly castellated whereby said segments are adapted to be inserted axially into said annular groove and rotated to an interference position where said segments are fixed axially with respect to said rotor.

8. The bladed rotor as defined in claim 6 wherein said radial walls are castellated and wherein the inner margins on said segments are matingly castellated whereby said segments are adapted to be inserted axially into said annular groove and rotated to an interference position where said segments are fixed axially with respect to said rotor.

9. The bladed rotor as defined in claim 8 wherein said means to prevent relative rotation between said segment and said rotor is a tab depending from the inner circumference of one of said elongated segments between a pair of adjacent castellations thereon and is disposed between a pair of adjacent castellations on said radial wall.

No references cited.

MARTIN P. SCHWADRON, Primary Examiner. E. A. POWELL, IR., Assistant Examiner, 

1. A BLADED ROTOR COMPRISING IN COMBINATION: A ROTOR HAVING A RIM WITH A PLURALITY OF CIRCUMFERENTIALLY SPACED GENERALLY AXIAL FIR TREE GROOVES, A PLURALITY OF BLADES HAVING FIR TREE ROOTS MOUNTED IN SAID GROOVES, EACH OF SAID BLADES HAVING A RADIALLY INWARDLY OPENING GROOVE SPACED RADIALLY OUTWARDLY OF ITS ROOT, AN AXIALLY EXTENDING CIRCUMFERENTIAL FLANGE ON SAID RIM SPACED INWARDLY OF SAID MOUNTING GROOVES, AN ANNULAR COVER PLATE MOUNTED ON SAID ROTOR AND HAVING ITS OUTER MARGIN DISPOSED IN SAID BLADE GROOVES AND ITS INNER EDGE ADJACENT SAID FLANGE, SAID COVER PLATE COMPRISING A PLURALITY OF ARCUTE SEGMENTS, EACH OF SAID SEGMENTS HAVING END SURFACES ABUTTING END SURFACES ON ADJACENT SEGMENTS TO FORM A CONTINUOUS ANNULUS, AT LEAST ONE OF SAID END SURFACES ON EACH OF SAID SEGMENTS BEING SKEWED WITH RESPECT TO THE RADIUS OF SAID ROTOR AND ABUTTING A MATING SKEWED END SURFACE ON AN ADJUSTMENT SEGMENT WHEREBY SAID COVER PLATE ACCOMMODATES DIFFERENTIAL THERMAL GROWTH BETWEEN SAID COVER PLATE AND SAID ROTOR AND BLADES. 